The invention relates to a blank and a method for preparing artificial tooth parts as well as a method manufacturing the blank.
The preparation of dental reconstructions, such as crowns or bridges, is usually carried out in the dental laboratory because prostheses having the required stability can only be prepared by combining a strong, load carrying material and weaker veneering materials, which requires several manufacturing steps. Such reconstructions are difficult to prepare.
The conventional state of the art method is the preparation of dental reconstruction bodies from a compound material, especially in the form of the porcelain fused to metal (PFM) reconstruction. In this method a supporting basic structure of metal is fitted, using a cast technique, to a tooth model obtained by dental preparation. The shape and color of the tooth are then added by burning ceramic material manually onto the basic structure. The combination of the highly tensile carrier material with a finish defining the color has proved to be successful as a durable method of reconstruction.
Lately, manual (Celay) and computer controlled (Cerec and other) methods have become known, by means of which dental reconstructions and parts of reconstructions can be prepared by grinding blanks out of single phase porcelain and ceramic material or polymer and composite material in a single step process, see e.g. W. H. Mormann, M. Brandestini, "Die CEREC Computer Reconstruction", 1989, Quintessenz Verlags-GmbH, Berlin, ISBN 3-87652-550-0. For example, blanks of feldspathic porcelain are used in the Cerec technique for producing inlays, onlays and veneers, as described in EP 160 797 A.
In a different method as described in EP 482 000 A, color layered blocks of plastic are suggested for preparing complete artificial teeth by abrasive machining using the Hennson/Sopha CAD/CAM-grinding technique. The prefabricated layer arrangement is selectively removed using reference information. Other grinding and milling techniques mainly prepare metal copings and parts of bridges for subsequent veneering with ceramics (DCS). These restaurations are designed for macromechanical retention and can be incorporated conventionally using zinc phosphate cement.
In an other method alumina blanks of porously sintered aluminum oxide or spinell ceramics respectively are shaped using the Cerec or Celay grinding techniques. The resulting shaped parts with open porous structure are then hot infiltrated (In-Ceram technique) with glass (lanthanum glasses), whereby a stability suitable for crowns and bridges is achieved.
The methods for manufacturing artificial tooth parts mentioned so far require a plurality of steps for preparing crowns or bridges, i.e. extra-coronal reconstructions, because these consist of at least two materials, one of which guarantees solidity and an other, weaker provides the natural dental color.